Wide ratio transmissions with a fixed interconnecting member and at least six clutches

ABSTRACT

The family of transmissions has a plurality of members that can be utilized in powertrains to provide at least eight forward speed ratios and one reverse speed ratio. The transmission family members include three planetary gear sets having seven torque-transmitting mechanisms and a fixed interconnecting member. The powertrain includes an engine and torque converter that is continuously connected to at least one of the planetary gear members and an output member that is continuously connected with another one of the planetary gear members. The seven torque-transmitting mechanisms provide interconnections between various gear members and the transmission housing, and are operated in combinations of three to establish at least eight forward speed ratios and at least one reverse speed ratio.

TECHNICAL FIELD

The present invention relates to a family of power transmissions having three planetary gear sets that are controlled by seven torque-transmitting devices to provide at least eight forward speed ratios and at least one reverse speed ratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point during cruising, other than the most efficient point. Therefore, manually-shifted (countershaft transmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improved the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.

It has been suggested that the number of forward speed ratios be increased to six or more. Six-speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978; and U.S. Pat. No. 6,422,969 issued to Raghavan and Usoro on Jul. 23, 2002.

Six-speed transmissions offer several advantages over four- and five-speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ power transmissions having six or more forward speed ratios, passenger cars are still manufactured with three- and four-speed automatic transmissions and relatively few five or six-speed devices due to the size and complexity of these transmissions.

Seven-speed transmissions are disclosed in U.S. Pat. No. 6,623,397 issued to Raghavan, Bucknor and Usoro. Eight speed transmissions are disclosed in U.S. Pat. No. 6,425,841 issued to Haka. The Haka transmission utilizes three planetary gear sets and six torque transmitting devices, including two brakes and two clutches, to provide eight forward speed ratios and a reverse speed ratio. One of the planetary gear sets is positioned and operated to establish two fixed speed input members for the remaining two planetary gear sets. The Haka transmission requires two double-transition shifts. Seven-, eight- and nine-speed transmissions provide further improvements in acceleration and fuel economy over six-speed transmissions. However, like the six-speed transmissions discussed above, the development of seven-, eight- and nine-speed transmissions has been precluded because of complexity, size and cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved family of transmissions having three planetary gear sets controlled to provide at least eight forward speed ratios and at least one reverse speed ratio.

In one aspect of the present invention, the family of transmissions has three planetary gear sets, each of which includes a first, second and third member, which members may comprise a sun gear, a ring gear, or a planet carrier assembly member.

In referring to the first, second and third gear sets in this description and in the claims, these sets may be counted “first” to “third” in any order in the drawings (i.e., left to right, right to left, etc.).

In another aspect of the present invention, each of the planetary gear sets may be of the single pinion-type or of the double pinion-type.

In yet another aspect of the present invention, a first member of the second planetary gear set is continuously interconnected with a first member of the third planetary gear set and with a stationary member through a first interconnecting member.

In yet a further aspect of the invention, each family member incorporates an input shaft which is continuously connected with a member of the planetary gear sets, and an output shaft which is continuously connected with another member of the planetary gear sets.

In still a further aspect of the invention, a first torque-transmitting mechanism, such as a clutch, selectively interconnects a member of the first planetary gear set with a member of the second planetary gear set.

In another aspect of the invention, a second torque-transmitting mechanism, such as a clutch, selectively interconnects a member of the first-planetary gear set with a member of the third planetary gear set.

In a still further aspect of the invention, a third torque-transmitting mechanism, such as a clutch, selectively interconnects a member of the second planetary gear set with a member of the first planetary gear set.

In a still further aspect of the invention, a fourth torque-transmitting mechanism, such as a clutch, selectively interconnects a member of the second planetary gear set with a member of the third planetary gear set.

In a still further aspect of the invention, a fifth torque-transmitting mechanism, such as a clutch, selectively interconnects a member of the third planetary gear set with a member of the first or second planetary gear set.

In still another aspect of the invention, a sixth torque-transmitting mechanism, such as a clutch, selectively interconnects a member of the first, second or third planetary gear set with another member of the first, second or third planetary gear sets.

In still another aspect of the invention, a seventh torque-transmitting mechanism, such as a clutch, selectively interconnects a member of the first, second or third planetary gear set with another member of the first, second or third planetary gear set. Alternatively, the seventh torque-transmitting mechanism, such as a brake, selectively connects a member of the first, second or third planetary gear set with the stationary member (transmission case).

In still another aspect of the invention, the seven torque-transmitting mechanisms are selectively engageable in combinations of three to yield at least eight forward speed ratios and at least one reverse speed ratio.

The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic representation of a powertrain including a planetary transmission incorporating a family member of the present invention;

FIG. 1 b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 1 a;

FIG. 2 a is a schematic representation of a powertrain having a planetary transmission incorporating another family member of the present invention;

FIG. 2 b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 2 a;

FIG. 3 a is a schematic representation of a powertrain having a planetary transmission incorporating another family member of the present invention;

FIG. 3 b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 3 a;

FIG. 4 a is a schematic representation of a powertrain having a planetary transmission incorporating another family member of the present invention;

FIG. 4 b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 4 a;

FIG. 5 a is a schematic representation of a powertrain having a planetary transmission incorporating another family member of the present invention;

FIG. 5 b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 5 a;

FIG. 6 a is a schematic representation of a powertrain having a planetary transmission incorporating another family member of the present invention;

FIG. 6 b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 6 a;

FIG. 7 a is a schematic representation of a powertrain having a planetary transmission incorporating another family member of the present invention;

FIG. 7 b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 7 a;

FIG. 8 a is a schematic representation of a powertrain having a planetary transmission incorporating another family member of the present invention;

FIG. 8 b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 8 a;

FIG. 9 a is a schematic representation of a powertrain having a planetary transmission incorporating another family member of the present invention; and

FIG. 9 b is a truth table and chart depicting some of the operating characteristics of the powertrain shown in FIG. 9 a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like characters represent the same or corresponding parts throughout the several views, there is shown in FIG. 1 a a powertrain 10 having a conventional engine and torque converter 12, a planetary transmission 14, and a conventional final drive mechanism 16.

The planetary transmission 14 includes an input shaft 17 continuously connected with the engine and torque converter 12, a planetary gear arrangement 18, and an output shaft 19 continuously connected with the final drive mechanism 16. The planetary gear arrangement 18 includes three planetary gear sets 20, 30 and 40.

The planetary gear set 20 includes a sun gear member 22, a ring gear member 24, and a planet carrier assembly 26. The planet carrier assembly 26 includes a plurality of pinion gears 27 rotatably mounted on a carrier member 29 and disposed in meshing relationship with both the sun gear member 22 and the ring gear member 24.

The planetary gear set 30 includes a sun gear member 32, a ring gear member 34, and a planet carrier assembly member 36. The planet carrier assembly member 36 includes a plurality of pinion gears 37 rotatably mounted on a carrier member 39 and disposed in meshing relationship with both the sun gear member 32 and the ring gear member 34.

The planetary gear set 40 includes a sun gear member 42, a ring gear member 44, and a planet carrier assembly member 46. The planet carrier assembly member 46 includes a plurality of pinion gears 47 rotatably mounted on a carrier member 49 and disposed in meshing relationship with both the sun gear member 42 and the ring gear member 44.

The planetary gear arrangement also includes seven torque-transmitting mechanisms 50, 52, 54, 56, 57, 58 and 59. The torque-transmitting mechanisms 50, 52, 54, 56 and 58 are rotating-type torque-transmitting mechanisms, commonly termed clutches. The torque-transmitting mechanism 59 is a stationary-type torque transmitting mechanism, commonly termed brake or reaction clutch.

The input shaft 17 is continuously connected with the ring gear member 34, and the output shaft 19 is continuously connected with the ring gear member 24. The interconnecting member 70 continuously connects the sun gear member 32 and the sun gear member 42 with the transmission housing 60.

The clutch 50 selectively connects the sun gear member 22 with the ring gear member 34. The clutch 52 selectively connects the sun gear member 22 with the planet carrier assembly member 46. The clutch 54 selectively connects the sun gear member 22 with the ring gear member 44. The clutch 56 selectively connects the planet carrier assembly member 26 with the ring gear member 34. The clutch 57 selectively connects the planet carrier assembly member 26 with the planet carrier assembly member 46. The clutch 58 selectively connects the planet carrier assembly member 36 with the ring gear member 44. The brake 59 selectively connects the planet carrier assembly member 46 with the transmission housing 60.

As shown in FIG. 1 b, and in particular the truth table disclosed therein, the torque-transmitting mechanisms are selectively engaged in combinations of three to provide eight forward speed ratios (including an extra second speed ratio: 2′) and one reverse speed ratio.

The reverse speed ratio is established with the engagement of the clutches 50, 57 and the brake 59. The clutch 50 connects the sun gear member 22 with the ring gear member 34. The clutch 57 connects the planet carrier assembly member 26 with the planet carrier assembly member 46. The brake 59 connects the planet carrier assembly member 46 with the transmission housing 60. The planetary gear set 40, gear member 32 and planet carrier assembly member 26 do not rotate. The ring gear member 34 and sun gear member 22 rotate at the same speed as the input shaft 17. The ring gear member 24 rotates at the same speed as the output shaft 19. The ring gear member 24, and therefore the output shaft 19, rotates at a speed determined from the speed of the sun gear member 22 and the ring gear/sun gear tooth ratio of the planetary gear set 20. The numerical value of the reverse speed ratio is determined utilizing the ring gear/sun gear tooth ratio of the planetary gear set 20.

The first forward speed ratio is established with the engagement of the clutches 50, 57 and 58. The clutch 50 connects the sun gear member 22 with the ring gear member 34. The clutch 57 connects the planet carrier assembly member 26 with the planet carrier assembly member 46. The clutch 58 connects the planet carrier assembly member 36 with the ring gear member 44. The sun gear members 32, 42 do not rotate. The planet carrier assembly member 46 rotates at the same speed as the planet carrier assembly member 26. The ring gear member 44 rotates at the same speed as the planet carrier assembly member 36. The planet carrier assembly member 46 rotates at a speed determined from the speed of the ring gear member 44 and the ring gear/sun gear tooth ratio of the planetary gear set 40. The ring gear member 34 and sun gear member 22 rotate at the same speed as the input shaft 17. The speed of the planet carrier assembly member 36 is determined from the speed of the ring gear member 34 and the ring gear/sun gear tooth ratio of the planetary gear set 30. The ring gear member 24 rotates at the same speed as the output shaft 19. The ring gear member 24, and therefore the output shaft 19, rotates at a speed determined from the speed of the planet carrier assembly member 26, the speed of the sun gear member 22 and the ring gear/sun gear tooth ratio of the planetary gear set 20. The numerical value of the first forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets 20, 30 and 40.

The second forward speed ratio is established with the engagement of the clutches 54, 57 and 58. The clutch 54 connects the sun gear member 22 with the ring gear member 44. The clutch 57 connects the planet carrier assembly member 26 with the planet carrier assembly member 46. The clutch 58 connects the planet carrier assembly member 36 with the ring gear member 44. The sun gear members 42, 32 do not rotate. The planet carrier assembly member 46 rotates at the same speed as the planet carrier assembly member 26. The ring gear member 44, planet carrier assembly member 36, and sun gear member 22 rotate at the same speed. The speed of the planet carrier assembly member 46 is determined from the speed of the ring gear member 44 and the ring gear/sun gear tooth ratio of the planetary gear set 40. The ring gear member 34 rotates at the same speed as the input shaft 17. The speed of the planet carrier assembly member 36 is determined from the speed of the ring gear member 34 and the ring gear/sun gear tooth ratio of the planetary gear set 30. The ring gear member 24 rotates at the same speed as the output shaft 19. The ring gear member 24, and therefore the output shaft 19, rotates at a speed determined from the speed of the planet carrier assembly member 26, the speed of the sun gear member 22, and the ring gear/sun gear tooth ratio of the planetary gear set 20. The numerical value of the second forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets 20, 30 and 40.

The extra second forward speed ratio (2′) is established with the engagement of the clutches 52, 57 and 58. The clutch 52 connects the sun gear member 22 with the planet carrier assembly member 46. The clutch 57 connects the planet carrier assembly member 26 with the planet carrier assembly member 46. The clutch 58 connects the planet carrier assembly member 36 with the ring gear member 44. The sun gear members 42, 32 do not rotate. The planet carrier assembly member 46 rotates at the same speed as the planetary gear set 20 and the output shaft 19. The ring gear member 44 rotates at the same speed as the planet carrier assembly member 36. The speed of the planet carrier assembly member 46, and therefore the output shaft 19, is determined from the speed of the ring gear member 44 and the ring gear/sun gear tooth ratio of the planetary gear set 40. The ring gear member 34 rotates at the same speed as the input shaft 17. The speed of the planet carrier assembly member 36 is determined from the speed of the ring gear member 34 and the ring gear/sun gear tooth ratio of the planetary gear set 30. The numerical value of the extra second forward speed ratio (2′) is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets 30, 40.

The third forward speed ratio is established with the engagement of the clutches 50, 54 and 57. The clutch 50 connects the sun gear member 22 with the ring gear member 34. The clutch 54 connects the sun gear member 22 with the ring gear member 44. The clutch 57 connects the planet carrier assembly member 26 with the planet carrier assembly member 46. The sun gear members 42, 32 do not rotate. The planet carrier assembly member 46 rotates at the same speed as the planet carrier assembly member 26. The ring gear member 44, sun gear member 22 and ring gear member 34 rotate at the same speed as the input shaft 17. The planet carrier assembly member 46 rotates at a speed determined from the speed of the ring gear member 44 and the ring gear/sun gear tooth ratio of the planetary gear set 40. The ring gear member 24 rotates at the same speed as the output shaft 19. The ring gear member 24, and therefore the output shaft 19, rotates at a speed determined from the speed of the planet carrier assembly member 26, the speed of the sun gear member 22, and the ring gear/sun gear tooth ratio of the planetary gear set 20. The numerical value of the third forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets 20, 40.

The fourth forward speed ratio is established with the engagement of the clutches 54, 56 and 57. The clutch 54 connects the sun gear member 22 with the ring gear member 44. The clutch 56 connects the planet carrier assembly member 26 with the ring gear member 34. The clutch 57 connects the planet carrier assembly member 26 with the planet carrier assembly member 46. The sun gear members 42, 32 do not rotate. The planet carrier assembly members 46, 26 and the ring gear member 34 rotate at the same speed as the input shaft 17. The ring gear member 44 rotates at the same speed as the sun gear member 22. The ring gear member 44 rotates at a speed determined from the speed of the planet carrier assembly member 46 and the ring gear/sun gear tooth ratio of the planetary gear set 40. The ring gear member 24 rotates at the same speed as the output shaft 19. The ring gear member 24, and therefore the output shaft 19, rotates at a speed determined from the speed of the planet carrier assembly member 26, the speed of the sun gear member 22, and the ring gear/sun gear tooth ratio of the planetary gear set 20.

The fifth forward speed ratio is established with the engagement of the clutches 50, 54 and 56. In this configuration, the speed of the output shaft 19 is equal to the speed of the input shaft 17, therefore the numerical value of the fifth forward speed ratio is 1.

The sixth forward speed ratio is established with the engagement of the clutches 54, 56 and 58. The clutch 54 connects the sun gear member 22 with the ring gear member 44. The clutch 56 connects the planet carrier assembly member 26 with the ring gear member 34. The clutch 58 connects the planet carrier assembly member 36 with the ring gear member 44. The sun gear members 42, 32 do not rotate. The ring gear member 44 rotates at the same speed as the planet carrier assembly member 36 and the sun gear member 22. The ring gear member 34 and planet carrier assembly member 26 rotate at the same speed as the input shaft 17. The speed of the planet carrier assembly member 36 is determined from the speed of the ring gear member 34 and the ring gear/sun gear tooth ratio of the planetary gear set 30. The ring gear member 24 rotates at the same speed as the output shaft 19. The ring gear member 24, and therefore the output shaft 19, rotates at a speed determined from the speed of the planet carrier assembly member 26, the speed of the sun gear member 22, and the ring gear/sun gear tooth ratio of the planetary gear set 20. The numerical value of the sixth forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets 20 and 30.

The seventh forward speed ratio is established with the engagement of the clutches 52, 56 and 58. The clutch 52 connects the sun gear member 22 with the planet carrier assembly member 46. The clutch 56 connects the planet carrier assembly member 26 with the ring gear member 34. The clutch 58 connects the planet carrier assembly member 36 with the ring gear member 44. The sun gear members 42, 32 do not rotate. The planet carrier assembly member 46 rotates at the same speed as the sun gear member 22. The ring gear member 44 rotates at the same speed as the planet carrier assembly member 36. The planet carrier assembly member 46 rotates at a speed determined from the speed of the ring gear member 44 and the ring gear/sun gear tooth ratio of the planetary gear set 40. The ring gear member 34 and the planet carrier assembly member 26 rotate at the same speed as the input shaft 17. The planet carrier assembly member 36 rotates at a speed determined from the speed of the ring gear member 34 and the ring gear/sun gear tooth ratio of the planetary gear set 30. The ring gear member 24 rotates at the same speed as the output shaft 19. The ring gear member 24, and therefore the output shaft 19, rotates at a speed determined from the speed of the planet carrier assembly member 26, the speed of the sun gear member 22, and the ring gear/sun gear tooth ratio of the planetary gear set 20. The numerical value of the seventh forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets 20, 30 and 40.

The eighth forward speed ratio is established with the engagement of the clutches 52, 56 and the brake 59. The clutch 52 connects the sun gear member 22 with the planet carrier assembly member 46. The clutch 56 connects the planet carrier assembly member 26 with the ring gear member 34. The brake 59 connects the planet carrier assembly member 46 with the transmission housing 60. The planetary gear set 40 and sun gear members 32, 22 do not rotate. The ring gear member 34 and planet carrier assembly member 26 rotate at the same speed as the input shaft 17. The ring gear member 24 rotates at the same speed as the output shaft 19. The ring gear member 24, and therefore the output shaft 19, rotates at a speed determined from the speed of the planet carrier assembly member 26 and the ring gear/sun gear tooth ratio of the planetary gear set 20. The numerical value of the eighth forward speed ratio is determined utilizing the ring gear/sun gear tooth ratio of the planetary gear set 20.

As set forth above, the engagement schedule for the torque-transmitting mechanisms is shown in the truth table of FIG. 1 b. This truth table also provides an example of speed ratios that are available utilizing the ring gear/sun gear tooth ratios given by way of example in FIG. 1 b. The N_(R1)/N_(S1) value is the tooth ratio of the planetary gear set 20; the N_(R2)/N_(S2) value is the tooth ratio of the planetary gear set 30; and the N_(R3)/N_(S3) value is the tooth ratio of the planetary gear set 40. Also, the chart of FIG. 1 b describes the ratio steps that are attained utilizing the sample of tooth ratios given. For example, the step ratio between the first and second forward speed ratios is 1.65, while the step ratio between the reverse and first forward ratio is −0.50.

FIG. 2 a shows a powertrain 110 having a conventional engine and torque converter 12, a planetary transmission 114, and a conventional final drive mechanism 16.

The planetary transmission 114 includes an input shaft 17 continuously connected with the engine and torque converter 12, a planetary gear arrangement 118, and an output shaft 19 continuously connected with the final drive mechanism 16. The planetary gear arrangement 118 includes three planetary gear sets 120, 130 and 140.

The planetary gear set 120 includes a sun gear member 122, a ring gear member 124, and a planet carrier assembly 126. The planet carrier assembly 126 includes a plurality of pinion gears 127 rotatably mounted on a carrier member 129 and disposed in meshing relationship with both the sun gear member 122 and the ring gear member 124.

The planetary gear set 130 includes a sun gear member 132, a ring gear member 134, and a planet carrier assembly member 136. The planet carrier assembly member 136 includes a plurality of pinion gears 137 rotatably mounted on a carrier member 139 and disposed in meshing relationship with both the sun gear member 132 and the ring gear member 134.

The planetary gear set 140 includes a sun gear member 142, a ring gear member 144, and a planet carrier assembly member 146. The planet carrier assembly member 146 includes a plurality of pinion gears 147 rotatably mounted on a carrier member 149 and disposed in meshing relationship with both the sun gear member 142 and the ring gear member 144.

The planetary gear arrangement 118 also includes seven torque-transmitting mechanisms 150, 152, 154, 156, 157, 158 and 159. The torque-transmitting mechanisms 150, 152, 154, 156, 157, 158 and 159 are all rotating-type torque-transmitting mechanisms, commonly termed clutches.

The input shaft 17 is continuously connected with the planet carrier assembly member 126, and the output shaft 19 is continuously connected with the ring gear member 124. The interconnecting member 170 continuously connects the sun gear member 132 and ring gear member 144 with the transmission housing 160.

The clutch 150 selectively connects the planet carrier assembly member 126 with the ring gear member 134. The clutch 152 selectively connects the planet carrier assembly member 126 with the planet carrier assembly member 136. The clutch 154 selectively connects the planet carrier assembly member 126 with the planet carrier assembly member 146. The clutch 156 selectively connects the sun gear member 122 with the ring gear member 134. The clutch 157 selectively connects the sun gear member 122 with the sun gear member 142. The clutch 158 selectively connects the ring gear member 124 with the planet carrier assembly member 146. The clutch 159 selectively connects the planet carrier assembly member 136 with the sun gear member 142.

The truth table of FIG. 2 b describes the engagement sequence utilized to provide eight forward speed ratios and two reverse speed ratios in the planetary gear arrangement 118 shown in FIG. 2 a.

The truth tables given in FIGS. 2 b, 3 b, 4 b, 5 b, 6 b, 7 b, 8 b and 9 b show the engagement sequences for the torque-transmitting mechanisms to provide at least eight forward speed ratios and at least one reverse ratio. As shown and described above for the configuration in FIG. 1 a, those skilled in the art will understand from the respective truth tables how the speed ratios are established through the planetary gear sets identified in the written description.

As set forth above, the truth table of FIG. 2 b describes the engagement sequence of the torque-transmitting mechanisms utilized to provide two reverse drive ratios and eight forward speed ratios. The truth table also provides an example of the ratios that can be attained with the family members shown in FIG. 2 a utilizing the sample tooth ratios given in FIG. 2 b. The N_(R1)/NS, value is the tooth ratio of the planetary gear set 120; the N_(R2)/N_(S2) value is the tooth ratio of the planetary gear set 130; and the N_(R3)/N_(S3) value is the tooth ratio of the planetary gear set 140. Also shown in FIG. 2 b are the ratio steps between single step ratios in the forward direction as well as the reverse to first ratio step ratio. For example, the first to second step ratio is 1.50.

Turning to FIG. 3 a, a powertrain 210 includes the engine and torque converter 12, a planetary transmission 214, and a final drive mechanism 16. The planetary transmission 214 includes an input shaft 17 continuously connected with the engine and torque converter 12, a planetary gear arrangement 218, and an output shaft 19 continuously connected with the final drive mechanism 16. The planetary gear arrangement 218 includes three planetary gear sets 220, 230 and 240.

The planetary gear set 220 includes a sun gear member 222, a ring gear member 224, and a planet carrier assembly 226. The planet carrier assembly 226 includes a plurality of pinion gears 227 rotatably mounted on a carrier member 229 and disposed in meshing relationship with both the sun gear member 222 and the ring gear member 224.

The planetary gear set 230 includes a sun gear member 232, a ring gear member 234, and a planet carrier assembly member 236. The planet carrier assembly member 236 includes a plurality of pinion gears 237 rotatably mounted on a carrier member 239 and disposed in meshing relationship with both the sun gear member 232 and the ring gear member 234.

The planetary gear set 240 includes a sun gear member 242, a ring gear member 244, and a planet carrier assembly member 246. The planet carrier assembly member 246 includes a plurality of pinion gears 247 rotatably mounted on a carrier member 249 and disposed in meshing relationship with both the sun gear member 242 and the ring gear member 244.

The planetary gear arrangement 218 also includes seven torque-transmitting mechanisms 250, 252, 254, 256, 257, 258 and 259. The torque-transmitting mechanisms 250, 252, 254, 256, 257 and 258 are rotating type torque-transmitting mechanisms, commonly termed clutches. The torque-transmitting mechanism 259 is a stationary-type torque transmitting mechanism, commonly termed brake or reaction clutch.

The input shaft 17 is continuously connected with the sun gear member 232, and the output shaft 19 is continuously connected with the ring gear member 224. The interconnecting member 270 continuously connects the ring gear member 234 and sun gear member 242 with the transmission housing 260.

The clutch 250 selectively connects the sun gear member 222 with the planet carrier assembly member 236. The clutch 252 selectively connects the sun gear member 222 with the sun gear member 232. The clutch 254 selectively connects the sun gear member 222 with the ring gear member 244. The clutch 256 selectively connects the planet carrier assembly member 226 with the sun gear member 232. The clutch 257 selectively connects the planet carrier assembly member 226 with the planet carrier assembly member 246. The clutch 258 selectively connects the planet carrier assembly member 236 with the planet carrier assembly member 246. The brake 259 selectively connects the planet carrier assembly member 246 with the transmission housing 260.

As shown in the truth table in FIG. 3 b, the torque-transmitting mechanisms are engaged in combinations of three to establish eight forward speed ratios (including extra first and second speed ratios: 1′, 2′), and two reverse speed ratios.

As previously set forth, the truth table of FIG. 3 b describes the combinations of engagements utilized for the forward and reverse speed ratios. The truth table also provides an example of speed ratios that are available with the family member described above. These examples of speed ratios are determined utilizing the tooth ratios given in FIG. 3 b. The N_(R1)/N_(S1) value is the tooth ratio of the planetary gear set 220; the N_(R2)/N_(S2) value is the tooth ratio of the planetary gear set 230; and the N_(R3)/N_(S3) value is the tooth ratio of the planetary gear set 240. Also depicted in FIG. 3 b is a chart representing the ratio steps between adjacent forward speed ratios and between the first and the reverse #2 speed ratio. For example, the first to second ratio interchange has a step of 1.50.

A powertrain 310, shown in FIG. 4 a, includes the engine and torque converter 12, a planetary transmission 314, and the final drive mechanism 16. The planetary transmission 314 includes an input shaft 17 continuously connected with the engine and torque converter 12, a planetary gear arrangement 318, and output shaft 19 continuously connected with the final drive mechanism 16. The planetary gear arrangement 318 includes three planetary gear sets 320, 330 and 340.

The planetary gear set 320 includes a sun gear member 322, a ring gear member 324, and a planet carrier assembly member 326. The planet carrier assembly member 326 includes a plurality of pinion gears 327 rotatably mounted on a carrier member 329 and disposed in meshing relationship with both the sun gear member 322 and the ring gear member 324.

The planetary gear set 330 includes a sun gear member 332, a ring gear member 334, and a planet carrier assembly member 336. The planet carrier assembly member 336 includes a plurality of pinion gears 337 rotatably mounted on a carrier member 339 and disposed in meshing relationship with both the sun gear member 332 and the ring gear member 334.

The planetary gear set 340 includes a sun gear member 342, a ring gear member 344, and a planet carrier assembly member 346. The planet carrier assembly member 346 includes a plurality of pinion gears 347 rotatably mounted on a carrier member 349 and disposed in meshing relationship with both the sun gear member 342 and the ring gear member 344.

The planetary gear arrangement 318 also includes seven torque-transmitting mechanisms 350, 352, 354, 356, 357, 358 and 359. The torque-transmitting mechanisms 350, 352, 354, 356, 357 and 358 are rotating type torque-transmitting mechanisms, commonly termed clutches. The torque-transmitting mechanism 359 is a stationary-type torque transmitting mechanism, commonly termed brake or reaction clutch.

The input shaft 17 is continuously connected with the sun gear member 332, and the output shaft 19 is continuously connected with the ring gear member 324. The interconnecting member 370 continuously connects the ring gear member 334 and sun gear member 342 with the transmission housing 360.

The clutch 350 selectively connects the planet carrier assembly member 326 with the sun gear member 332. The clutch 352 selectively connects the planet carrier assembly member 326 with the planet carrier assembly member 346. The clutch 354 selectively connects the sun gear member 322 with the sun gear member 332. The clutch 354 selectively connects the sun gear member 322 with the ring gear member 344. The clutch 357 selectively connects the planet carrier assembly member 336 with the planet carrier assembly member 346. The clutch 358 selectively connects the planet carrier assembly member 336 with the ring gear member 344. The brake 359 selectively connects the planet carrier assembly member 346 with the transmission housing 360.

The truth table shown in FIG. 4 b describes the engagement combination and the engagement sequence necessary to provide two reverse drive ratios and eight forward speed ratios. A sample of the numerical values for the ratios is also provided in the truth table of FIG. 4 b. These values are determined utilizing the ring gear/sun gear tooth ratios also given in FIG. 4 b. The N_(R1)/NS, value is the tooth ratio for the planetary gear set 320; the N_(R2)/N_(S2) value is the tooth ratio for the planetary gear set 330; and the N_(R3)/N_(S3) value is the tooth ratio for the planetary gear set 340. Also given in FIG. 4 b is a chart describing the step ratios between the adjacent forward speed ratios and the reverse #2 to first forward speed ratio. For example, the first to second forward speed ratio step is 1.46.

A powertrain 410, shown in FIG. 5 a, includes the engine and torque converter 12, a planetary transmission 414 and the final drive mechanism 16. The planetary transmission 414 includes a planetary gear arrangement 418, input shaft 17 and output shaft 19. The planetary gear arrangement 418 includes three simple planetary gear sets 420, 430 and 440.

The planetary gear set 420 includes a sun gear member 422, a ring gear member 424, and a planet carrier assembly 426. The planet carrier assembly 426 includes a plurality of pinion gears 427 rotatably mounted on a carrier member 429 and disposed in meshing relationship with both the sun gear member 422 and the ring gear member 424.

The planetary gear set 430 includes a sun gear member 432, a ring gear member 434, and a planet carrier assembly member 436. The planet carrier assembly member 436 includes a plurality of pinion gears 437, 438 rotatably mounted on a carrier member 439 and disposed in meshing relationship with the the ring gear member 434 and sun gear member 432, respectively.

The planetary gear set 440 includes a sun gear member 442, a ring gear member 444, and a planet carrier assembly member 446. The planet carrier assembly member 446 includes a plurality of pinion gears 447 rotatably mounted on a carrier member 449 and disposed in meshing relationship with both the sun gear member 442 and the ring gear member 444.

The planetary gear arrangement 418 also includes seven torque-transmitting mechanisms 450, 452, 454, 456, 457, 458 and 459. The torque-transmitting mechanisms 450, 452, 454, 456, 457, 458 and 459 are all rotating type torque-transmitting mechanisms, commonly termed clutches.

The input shaft 17 is continuously connected with the sun gear member 432, and the output shaft 19 is continuously connected with the ring gear member 424. The interconnecting member 470 continuously connects the planet carrier assembly member 436 and the sun gear member 442 with the transmission housing 460.

The clutch 450 selectively connects the sun gear member 422 with the sun gear member 432. The clutch 452 selectively connects the sun gear member 422 with the planet carrier assembly member 446. The clutch 454 selectively connects the sun gear member 422 with the ring gear member 444. The clutch 456 selectively connects the planet carrier assembly member 426 with the sun gear member 432. The clutch 457 selectively connects the planet carrier assembly member 426 with the planet carrier assembly member 446. The clutch 458 selectively connects the ring gear member 434 with the planet carrier assembly member 446. The clutch 459 selectively connects the ring gear member 434 with the ring gear member 444.

The truth table shown in FIG. 5 b describes the engagement combination and sequence of the torque-transmitting mechanisms 450, 452, 454, 456, 457, 458 and 459 that are employed to provide the forward and reverse drive ratios.

Also given in the truth table of FIG. 5 b is a set of numerical values that are attainable with the present invention utilizing the ring gear/sun gear tooth ratios shown. The N_(R1)/N_(S1) value is the tooth ratio of the planetary gear set 420; the N_(R2)/N_(S2) value is the tooth ratio of the planetary gear set 430; and the N_(R3)/N_(S3) value is the tooth ratio of the planetary gear set 440.

FIG. 5 b also provides a chart of the ratio steps between adjacent forward ratios and between the reverse and first forward ratio. For example, the ratio step between the first and second forward ratios is 1.46.

A powertrain 510, shown in FIG. 6 a, includes an engine and torque converter 12, a planetary gear transmission 514 and the final drive mechanism 16. The planetary transmission 514 includes the input shaft 17, a planetary gear arrangement 518 and the output shaft 19. The planetary gear arrangement 518 includes three planetary gear sets 520, 530 and 540.

The planetary gear set 520 includes a sun gear member 522, a ring gear member 524, and a planet carrier assembly 526. The planet carrier assembly 526 includes a plurality of pinion gears 527 rotatably mounted on a carrier member 529 and disposed in meshing relationship with both the sun gear member 522 and the ring gear member 524.

The planetary gear set 530 includes a sun gear member 532, a ring gear member 534, and a planet carrier assembly member 536. The planet carrier assembly member 536 includes a plurality of pinion gears 537 rotatably mounted on a carrier member 539 and disposed in meshing relationship with both the sun gear member 532 and the ring gear member 534.

The planetary gear set 540 includes a sun gear member 542, a ring gear member 544, and a planet carrier assembly member 546. The planet carrier assembly member 546 includes a plurality of pinion gears 547 rotatably mounted on a carrier member 549 and disposed in meshing relationship with both the sun gear member 542 and the ring gear member 544.

The planetary gear arrangement 518 also includes seven torque-transmitting mechanisms 550, 552, 554, 556, 557, 558 and 559. The torque-transmitting mechanisms 550, 552, 554, 556, 557 and 558 are rotating type torque-transmitting mechanisms, commonly termed clutches. The torque-transmitting mechanism 559 is a stationary-type torque transmitting mechanism, commonly termed brake or reaction clutch.

The input shaft 17 is continuously connected with the ring gear member 534, and the output shaft 19 is continuously connected with the ring gear member 524. The interconnecting member 570 continuously connects the sun gear members 532 and 542 with the transmission housing 560.

The clutch 550 selectively connects the planet carrier assembly member 526 with the ring gear member 534. The clutch 552 selectively connects the planet carrier assembly member 526 with the planet carrier assembly member 546. The clutch 554 selectively connects the sun gear member 522 with the ring gear member 534. The clutch 556 selectively connects the sun gear member 522 with the planet carrier assembly member 546. The clutch 557 selectively connects the sun gear member 522 with the ring gear member 544. The clutch 558 selectively connects the planet carrier assembly member 536 with the ring gear member 544. The brake 559 selectively connects the planet carrier assembly member 526 with the transmission housing 560.

The truth table shown in FIG. 6 b describes the engagement sequence and combination of the torque-transmitting mechanisms to provide the three reverse speed ratios and eight forward speed ratios (and the extra second speed ratio: 2′). The chart of FIG. 6 b describes the ratio steps between adjacent forward speed ratios and the ratio step between the reverse #3 and first forward speed ratio.

The sample speed ratios given in the truth table are determined utilizing the tooth ratio values also given in FIG. 6 b. The N_(R1)/N_(S1) value is the tooth ratio of the planetary gear set 520; the N_(R2)/N_(S2) value is the tooth ratio of the planetary gear set 530; and the N_(R3)/N_(S3) value is the tooth ratio of the planetary gear set 540.

A powertrain 610, shown in FIG. 7 a, has the engine and torque converter 12, a planetary transmission 614 and the final drive mechanism 16. The planetary transmission 614 includes the input shaft 17, a planetary gear arrangement 618 and the output shaft 19. The planetary gear arrangement 618 includes three planetary gear sets 620, 630 and 640.

The planetary gear set 620 includes a sun gear member 622, a ring gear member 624, and a planet carrier assembly 626. The planet carrier assembly 626 includes a plurality of pinion gears 627 rotatably mounted on a carrier member 629 and disposed in meshing relationship with both the sun gear member 622 and the ring gear member 624.

The planetary gear set 630 includes a sun gear member 632, a ring gear member 634, and a planet carrier assembly member 636. The planet carrier assembly member 636 includes a plurality of pinion gears 637 rotatably mounted on a carrier member 639 and disposed in meshing relationship with both the sun gear member 632 and the ring gear member 634.

The planetary gear set 640 includes a sun gear member 642, a ring gear member 644, and a planet carrier assembly member 646. The planet carrier assembly member 646 includes a plurality of pinion gears 647 rotatably mounted on a carrier member 649 and disposed in meshing relationship with both the sun gear member 642 and the ring gear member 644.

The planetary gear arrangement 618 also includes seven torque-transmitting mechanisms 650, 652, 654, 656, 657, 658 and 659. The torque-transmitting mechanisms 650, 652, 654, 656, 657 and 658 are rotating type torque-transmitting mechanisms, commonly termed clutches. The torque-transmitting mechanism 659 is a stationary-type torque transmitting mechanism, commonly termed brake or reaction clutch.

The input shaft 17 is continuously connected with the planet carrier assembly member 636. The output shaft 19 is continuously connected with the ring gear member 624. The interconnecting member 670 continuously connects the sun gear members 632 and 642 with the transmission housing 660.

The clutch 650 selectively connects the sun gear member 622 with the ring gear member 634. The clutch 652 selectively connects the sun gear member 622 with the planet carrier assembly member 646. The clutch 654 selectively connects the sun gear member 622 with the ring gear member 644. The clutch 656 selectively connects the planet carrier assembly member 626 with the ring gear member 634. The clutch 657 selectively connects the planet carrier assembly member 626 with the planet carrier assembly member 646. The clutch 658 selectively connects the planet carrier assembly member 636 with the ring gear member 644. The brake 659 selectively connects the planet carrier assembly member 646 with the transmission housing 660.

The truth table shown in FIG. 7 b describes the combination of torque-transmitting mechanism engagements that will provide the reverse drive ratio and eight forward speed ratios (including the extra second speed ratio: 2′), as well as the sequence of these engagements and interchanges. The torque-transmitting mechanisms 650 and 657 can be engaged through the neutral condition, thereby simplifying the forward/reverse interchange.

The ratio values given are by way of example and are established utilizing the ring gear/sun gear tooth ratios given in FIG. 7 b. For example, the N_(R1)/N_(S1) value is the tooth ratio of the planetary gear set 620; the N_(R2)/N_(S2) value is the tooth ratio of the planetary gear set 630; and the N_(R3)/N_(S3) value is the tooth ratio of the planetary gear set 640. The ratio steps between adjacent forward ratios and the reverse to first ratio are also given in FIG. 7 b.

A powertrain 710, shown in FIG. 8 a, has the conventional engine and torque converter 12, a planetary transmission 714, and the conventional final drive mechanism 16. The engine and torque converter 12 are drivingly connected with the planetary transmission 714 through the input shaft 17. The planetary transmission 714 is drivingly connected with the final drive mechanism 16 through the output shaft 19. The planetary transmission 714 includes a planetary gear arrangement 718 that has a first planetary gear set 720, a second planetary gear set 730, and a third planetary gear set 740.

The planetary gear set 720 includes a sun gear member 722, a ring gear member 724, and a planet carrier assembly 726. The planet carrier assembly 726 includes a plurality of pinion gears 727 rotatably mounted on a carrier member 729. The pinion gears 727 are disposed in meshing relationship with the sun gear member 722 and the ring gear member 724.

The planetary gear set 730 includes a sun gear member 732, a ring gear member 734, and a planet carrier assembly member 736. The planet carrier assembly member 736 includes a plurality of pinion gears 737 rotatably mounted on a carrier member 739 and disposed in meshing relationship with both the sun gear member 732 and the ring gear member 734.

The planetary gear set 740 includes a sun gear member 742, a ring gear member 744, and a planet carrier assembly member 746. The planet carrier assembly member 746 includes a plurality of pinion gears 747 rotatably mounted on a carrier member 749 and disposed in meshing relationship with both the sun gear member 742 and the ring gear member 744.

The planetary gear arrangement 718 also includes seven torque-transmitting mechanisms 750, 752, 754, 756, 757, 758 and 759. The torque-transmitting mechanisms 750, 752, 754, 756, 757, 758 and 759 are all rotating type torque-transmitting mechanisms, commonly termed clutches.

The input shaft 17 is continuously connected with the planet carrier assembly member 726. The output shaft 19 is continuously connected with the ring gear member 724. The interconnecting member 770 continuously connects the ring gear member 734 and sun gear member 742 with the transmission housing 760.

The clutch 750 selectively connects the planet carrier assembly member 726 with the planet carrier assembly member 736. The clutch 752 selectively connects the planet carrier assembly member 726 with the ring gear member 744. The clutch 754 selectively connects the planet carrier assembly member 726 with the planet carrier assembly member 746. The clutch 756 selectively connects the sun gear member 722 with the sun gear member 732. The clutch 757 selectively connects the sun gear member 722 with the ring gear member 744. The clutch 758 selectively connects the ring gear member 724 with the planet carrier assembly member 736. The clutch 759 selectively connects the sun gear member 732 with the planet carrier assembly member 746.

The truth table of FIG. 8 b defines the torque-transmitting mechanism engagement sequence utilized for each of the forward and reverse speed ratios. Also given in the truth table is a set of numerical values that are attainable with the present invention utilizing the ring gear/sun gear tooth ratios given in FIG. 8 b. The N_(R1)/N_(S1) value is the tooth ratio of the planetary gear set 720; the N_(R2)/N_(S2) value is the tooth ratio of the planetary gear set 730; and the N_(R3)/N_(S3) value is the tooth ratio of the planetary gear set 740.

FIG. 8 b also provides a chart of the ratio steps between adjacent forward ratios and between the reverse #2 and first forward ratio. For example, the ratio step between the first and second forward ratios is 1.50.

A powertrain 810, shown in FIG. 9 a, has the conventional engine and torque converter 12, a planetary transmission 814, and the final drive mechanism 16. The engine and torque converter 12 are drivingly connected with the planetary transmission 814 through the input shaft 17. The planetary transmission 814 is drivingly connected with the final drive mechanism 16 through the output shaft 19. The planetary transmission 814 includes a planetary gear arrangement 818 that has a first planetary gear set 820, a second planetary gear set 830, and a third planetary gear set 840.

The planetary gear set 820 includes a sun gear member 822, a ring gear member 824, and a planet carrier assembly 826. The planet carrier assembly 826 includes a plurality of pinion gears 827 rotatably mounted on a carrier member 829 and disposed in meshing relationship with the sun gear member 822 and the ring gear member 824.

The planetary gear set 830 includes a sun gear member 832, a ring gear member 834, and a planet carrier assembly member 836. The planet carrier assembly member 836 includes a plurality of pinion gears 837 rotatably mounted on a carrier member 839 and disposed in meshing relationship with both the sun gear member 832 and the ring gear member 834.

The planetary gear set 840 includes a sun gear member 842, a ring gear member 844, and a planet carrier assembly member 846. The planet carrier assembly member 846 includes a plurality of pinion gears 847, 848 rotatably mounted on a carrier member 849 and disposed in meshing relationship with the ring gear member 844 and the sun gear member 842, respectively.

The planetary gear arrangement 818 also includes seven torque-transmitting mechanisms 850, 852, 854, 856, 857, 858 and 859. The torque-transmitting mechanisms 850, 852, 854, 856, 857, 858 and 859 are all rotating type torque-transmitting mechanisms, commonly termed clutches.

The input shaft 17 is continuously connected with the planet carrier assembly member 826. The output shaft 19 is continuously connected with the ring gear member 824. The interconnecting member 870 continuously connects the sun gear member 832 and planet carrier assembly member 846 with the transmission housing 860.

The clutch 850 selectively connects the planet carrier assembly member 826 with the ring gear member 834. The clutch 852 selectively connects the planet carrier assembly member 826 with the planet carrier assembly member 836. The clutch 854 selectively connects the planet carrier assembly member 826 with the ring gear member 844. The clutch 856 selectively connects the sun gear member 822 with the ring gear member 834. The clutch 857 selectively connects the sun gear member 822 with the sun gear member 842. The clutch 858 selectively connects the ring gear member 824 with the ring gear member 844. The clutch 859 selectively connects the planet carrier assembly member 836 with the sun gear member 842.

The truth table shown in FIG. 9 b defines the torque-transmitting mechanism engagement sequence that provides the two reverse speed ratios and eight forward speed ratios shown in the truth table and available with the planetary gear arrangement 818. A sample of numerical values for the individual ratios is also given in the truth table of FIG. 9 b. These numerical values have been calculated using the ring gear/sun gear tooth ratios also given by way of example in FIG. 9 b. The N_(R1)/N_(S1) value is the tooth ratio of the planetary gear set 820; the N_(R2)/N_(S2) value is the tooth ratio of the planetary gear set 830; and the N_(R3)/N_(S3) value is the tooth ratio of the planetary gear set 840. FIG. 9 b also describes the ratio steps between adjacent forward ratios and between the reverse and first forward ratio.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. 

1. A multi-speed transmission comprising: an input shaft; an output shaft; first, second and third planetary gear sets each having first, second and third members; said input shaft being continuously interconnected with a member of said planetary gear sets, and said output shaft being continuously interconnected with another member of said planetary gear sets; an interconnecting member continuously interconnecting said first member of said second planetary gear set with said first member of said third planetary gear set and with a stationary member; a first torque-transmitting mechanism selectively interconnecting a member of said first planetary gear set with a member of said second planetary gear set; a second torque-transmitting mechanism selectively interconnecting a member of said first planetary gear set with a member of said third planetary gear set; a third torque-transmitting mechanism selectively interconnecting a member of said second planetary gear set with a member of said first planetary gear set; a fourth torque-transmitting mechanism selectively interconnecting a member of said second planetary gear set with a member of said third planetary gear set; a fifth torque-transmitting mechanism selectively interconnecting a member of said third planetary gear set with a member of said first or second planetary gear set; a sixth torque-transmitting mechanism selectively interconnecting a member of said first, second or third planetary gear set with another member of said first, second or third planetary gear set; a seventh torque-transmitting mechanism selectively interconnecting a member of said first, second or third planetary gear set with another member of said first, second or third planetary gear set, or with said stationary member; said torque-transmitting mechanisms being engaged in combinations of three to establish at least eight forward speed ratios and at least one reverse speed ratio between said input shaft and said output shaft.
 2. The transmission defined in claim 1, wherein said first, second, third, fourth, fifth and sixth torque-transmitting mechanisms comprise clutches, and said seventh torque-transmitting mechanism comprises a brake.
 3. The transmission defined in claim 1, wherein said first, second, third, fourth, fifth, sixth and seventh torque-transmitting mechanisms comprise clutches.
 4. The transmission defined in claim 1, wherein planet carrier assembly members of each of said planetary gear sets are single-pinion carriers.
 5. The transmission defined in claim 1, wherein at least one planet carrier assembly member of said planetary gear sets is a double-pinion carrier.
 6. A multi-speed transmission comprising: an input shaft; an output shaft; a planetary gear arrangement having first, second and third planetary gear sets, each planetary gear set having first, second and third members; said input shaft being continuously interconnected with a member of said planetary gear sets, and said output shaft being continuously interconnected with another member of said planetary gear sets; an interconnecting member continuously interconnecting said first member of said second planetary gear set with said first member of said third planetary gear set and with a stationary member; and seven torque-transmitting mechanisms for selectively interconnecting said members of said planetary gear sets with said stationary member or with other members of said planetary gear sets, said seven torque-transmitting mechanisms being engaged in combinations of three to establish at least eight forward speed ratios and at least one reverse speed ratio between said input shaft and said output shaft.
 7. The transmission defined in claim 6, wherein a first of said seven torque-transmitting mechanisms is operable for selectively interconnecting a member of said first planetary gear set with a member of said second planetary gear set.
 8. The transmission defined in claim 6, wherein a second of said seven torque-transmitting mechanisms is operable for selectively interconnecting a member of said first planetary gear set with a member of said third planetary gear set.
 9. The transmission defined in claim 6, wherein a third of said seven torque-transmitting mechanisms is selectively operable for interconnecting a member of said second planetary gear set with a member of said first planetary gear set.
 10. The transmission defined in claim 6, wherein a fourth of said seven torque-transmitting mechanisms is selectively operable for interconnecting a member of said second planetary gear set with a member of said third planetary gear set.
 11. The transmission defined in claim 6, wherein a fifth of said seven torque-transmitting mechanisms is selectively operable for interconnecting a member of said third planetary gear set with a member of said first or second planetary gear set.
 12. The transmission defined in claim 6, wherein a sixth of said seven torque-transmitting mechanisms selectively interconnects a member of said first, second or third planetary gear set with another member of said first, second or third planetary gear set.
 13. The transmission defined in claim 6, wherein a seventh of said seven torque-transmitting mechanisms selectively interconnects a member of said first, second or third planetary gear set with another member of said first, second or third planetary gear set, or with said stationary member.
 14. The transmission defined in claim 6, wherein planet carrier assembly members of each of said planetary gear sets are single-pinion carriers.
 15. The transmission defined in claim 6, wherein at least one planet carrier assembly member of said planetary gear sets is a double-pinion carrier. 